Propidium monoazide (PMA) is a propidium derivative with an azide group th at allows crosslinkage to DNA upon light exposure. PMA is only permeable to bacteria with compromised membrane integrity, making it highly selective for sick/dying/dead cells over healthy cells. PMA is typically added to cell samples (50 μM for 1-15 min in the dark) prior to cross-linking induction (650-W halogen light source), washing and DNA extraction. Due to its higher charge, PMA (+2) is less permeant to live cells and more selective than ethidium monoazide/EMA (+1) for dead cells. The stained cells can also be viewed and analyzed by fluorescence microscopy.
